The present invention relates generally to circuitry used to correct asymmetric waveforms, such as those in disk drive signals, into symmetric waveforms.
The resistance of the sensing layer in a magnetoresistive (MR) head varies with the field in the vicinity of the heads. This feature is used to read data from magnetic disk drives. Ideally, the resistance of the sensing layer is a linear function of its magnetic orientation. In practice, however, the output of the MR head is asymmetric, owing to an offset in the biasing of the head. The percentage of asymmetry is defined as:       percentage    ⁢          xe2x80x83        ⁢    asymmetry    =                              "LeftBracketingBar"                      max            ⁢                          xe2x80x83                        ⁢            peak                    "RightBracketingBar"                -                  "LeftBracketingBar"                      min            ⁢                          xe2x80x83                        ⁢            peak                    "RightBracketingBar"                            "LeftBracketingBar"                  max          ⁢                      xe2x80x83                    ⁢          peak                "RightBracketingBar"              xc3x97    100  
Asymmetry could also be defined as:       percentage    ⁢          xe2x80x83        ⁢    asymmetry    =                              "LeftBracketingBar"                      max            ⁢                          xe2x80x83                        ⁢            peak                    "RightBracketingBar"                -                  "LeftBracketingBar"                      min            ⁢                          xe2x80x83                        ⁢            peak                    "RightBracketingBar"                                      (                                    "LeftBracketingBar"                              max                ⁢                                  xe2x80x83                                ⁢                peak                            "RightBracketingBar"                        +                          "LeftBracketingBar"                              min                ⁢                                  xe2x80x83                                ⁢                peak                            "RightBracketingBar"                                )                /        2              xc3x97    100  
Both the above definitions of asymmetry provide a quantitative way of expressing the degree of asymmetry in the waveform. The waveforms could be asymmetric with either polarity. The waveform is considered to be positively asymmetric if the positive side of the waveform has a higher peak than the negative side of the waveform. A waveform distorted in the opposite direction is considered negatively asymmetric. The asymmetric waveforms result in a high bit error rate (BER) being generated in the read channel electronics that process the signal from the MR head and extract data from this signal.
U.S. Pat. No. 6,043,943, entitled xe2x80x9cAsymmetry correction for a read head,xe2x80x9d (F. Rezzi, G. Patti, ST Microelectronics Inc., issued on Mar. 28, 2000), discloses an arrangement in which, in the context of correcting asymmetric waveforms, essentially one correction function is applied to both sides of a waveform. This often results in sub-optimal correction of the asymmetry at hand.
In view of the foregoing, a need has been recognized in connection with optimally converting asymmetric waveforms into symmetric waveforms in signal processing circuits or other environments in which such conversion would be appropriate or desirable.
In accordance with at least one presently preferred embodiment of the present invention, asymmetric waveforms are converted into symmetric waveforms via splitting the input signal into two rectified paths and applying correction independently on each of the paths.
In summary, one aspect of the invention provides an apparatus for correcting asymmetric waveforms, the apparatus comprising: an input arrangement which accepts an input signal, the input signal having an associated waveform; a splitting arrangement which splits the input signal into at least two paths; a first altering arrangement, associated with a first of the two signal paths, which alters a first portion of the split signal; a second altering arrangement, associated with a second of the two signal paths, which alters a second portion of the split signal; and an output arrangement which recombines the altered split signals into an output signal; whereby the output signal exhibits a substantially symmetric waveform.
Another aspect of the invention provides a method of correcting asymmetric waveforms, the method comprising the steps of: accepting an input signal, the input signal having an associated waveform; splitting the input signal into at least two portions; altering a first portion of the split signal; altering a second portion of the split signal; and recombining the altered split signals into an output signal; whereby the output signal exhibits a substantially symmetric waveform.
For a better understanding of the present invention, together with other and further features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, and the scope of the invention will be pointed out in the appended claims.